Population dynamics of marsh clam, Polymesoda spp. (Bivalvia: Corbiculidae) in Marudu Bay, Malaysia

Population parameters of Polymesoda erosa and P. expansa in Marudu Bay were estimated based on 1 year (June 2017 to May 2018) monthly length-weight frequency data. A total of 1087 and 2057 specimens of P. erosa and P. expansa, respectively were successfully collected and analysed. Results of the study demonstrated that the estimated asymptotic length (Linfi;), growth coefficient (K), total mortality (Z), natural mortality (M), fishing mortality (F) and growth performance (ф) of P. erosa were 92.4 mm, 0.76 yr-1, 2.22 yr-1, 0.76 yr-1, 1.44 yr-1 and 3.81 yr-1, respectively. The exponent b of the length-weight relationship was 2.27 and exploitation level (E) was 0.65. On the other hand, the asymptotic length (L ), growth coefficient (K), total mortality (Z), natural mortality (M), fishing mortality (F) and growth performance (ф) of P. expansa were 92.4 mm, 0.82 yr-1, 2.77 yr-1, 0.82 yr-1, 1.95 yr-1 and 3.85 yr-1, respectively. The exponent b of the length-weight relationship was 2.24 and exploitation level (e) was 0.7. The condition index of P. erosa and P. expansa were 2.28±0.49 and 2.31±0.67, respectively. It was also noted that both P. erosa and P. expansa exhibited continuous recruitment with the peak in June and November, respectively. However, they seemed to experience over-fishing as evidenced by the level of exploitation which was beyond the maximum sustainable yield (MSY). Hence, immediate implementation of a sustainable management plan is critically needed to ensure this resource remains viable in Marudu bay.